Siblinghood is the paradigm of horizontal links. When we talk about siblinghood we are not only referring to blood ties in families, but also to social ties in different stages of life. Siblinghood can include any relationships between peers which are participative and which involve horizontal rather than hierarchical links. To develop the concept of siblinghood we have drawn on the work of several authors regarding the fraternal complex. This article will also focus on the relevance of the fraternal complex in the context of institutional life and training. A short clinical vignette will be presented to show the effect of the fraternal complex on the relationship between a father and his young son.